The present invention relates to an image forming apparatus provided with an automatic original feeder for conveying an original with it being interposed between a transparent platen and original conveying means.
Conventionally, there has been known an electrophotographic copying apparatus provided with an automatic original feeder for automatically conveying an original to a transparent platen.
The above described automatic original feeder generally has a frame, original conveying means provided on this frame, and original feeding means for feeding an original to this original conveying means.
The above described frame is pivotable between such a closed position as to cover the transparent platen and such an opened position as to expose the transparent platen. The original feeding means is adjacent to the above described frame, and it feeds originals to the original conveying means one at a time. The original conveying means conveys the original fed by the original feeding means to a required position on the transparent platen and conveys the original from the transparent platen to the upper surface of the frame after exposing the original to light while scanning is terminated (see, for example, Japanese Patent Laid-Open Gazette No. 118551/1985). This original conveying means is constituted by an endless delivery belt mounted on almost the entire lower part of the frame.
On the other hand, in order to simplify the structure of the electrophotographic copying apparatus, the applicant of the present invention has proposed a delivery roller type automatic original feeder (see Japanese Patent Application No. 61333/1988). This automatic original feeder uses as the document conveying means a delivery roller which is mounted on the lower part of a frame and can abut on the upper surface of a transparent platen, which conveys an original to and from the transparent platen with it being interposed between this delivery roller and one end of the original platen according to forward and reverse rotation of the delivery roller.
However, in an electrophotographic copying apparatus of an intermediate degree or less, a frame is not a high strength frame made of steel or the like but of monocoque construction so as to simplify the structure and reduce the cost, so that the frame is liable to, for example, warped. Thus, this electrophotographic copying apparatus has the disadvantage in that an original can not be reliably conveyed because the pressure applied to the original by the original conveying means is changed due to, for example, the effect of the warping or the like and the variation in assembling precision.
In order to eliminate the disadvantage, there has been known an electrophotographic copying apparatus for adjusting the above described pressure by providing a height adjusting mechanism for adjusting the height of a frame from a transparent platen. In this electrophotographic copying apparatus, a supporting portion of the frame is fixed to a vertical plate provided on the main body thereof by a bolt and a nut and a portion penetrated by the bolt in the vertical plate is a slot. The above described height adjusting mechanism is used for adjusting the position in which the supporting portion is attached to the vertical plate. Accordingly, the adjustment must be carried out while lifting the frame, which is not easy. In addition, one of the bolt and the nut is arranged inside of the frame. Thus, the adjustment must be carried out with the frame being opened, which is troublesome.
Meanwhile, the above described delivery roller is arranged directly over the transparent platen at the time of conveying the original. Thus, the electrophotographic copying apparatus also has the disadvantage in that a good reproduced image can not be obtained because an outline or the like of the delivery roller is clearly copied on copy paper when the size of an original is so small that the delivery roller is forced out of the original in, for example, manually disposing the original or when an original permeable to light at the time of exposure to light such as a copy of a sheet for an OHP (Over Head Prejector) or a tracing paper is copied.
Furthermore, the above described image forming apparatus is generally provided with an original discharge passage in a predetermined position between the frame and the delivery roller and adapted to convey the original fed from the original feeding means through an original conveying passage to the transparent platen by forward rotation of the delivery roller as well as to convey the original from the transparent platen to the upper surface of the frame by way of the original discharge passage by reverse rotation of the delivery roller after termination of exposing the original to light while scanning.
Only an end of the above described transparent platen which is farther away from the original feeding means is pressurized to be fixed by a longitudinal fixing member. The reason is that it is difficult to convey the original from the transparent platen if an end of the transparent platen which is closer to the original feeding means is also fixed by the fixing member because the original is caught by the fixing member at the time of conveying the original from the transparent platen. In addition, the reason is that a guide member for introducing the original into the original discharge passage, which must be provided in the vicinity of the end of the transparent platen which is closer to the original feeding means, can not be provided in the end if the end is fixed by the above described fixing means.
Thus, the above described image forming apparatus also has the disadvantage in that the original is copied with an image forming position being shifted irrespective of accurately setting the original to a mark on the transparent platen because the position of the transparent platen is shifted due to the vibration caused at the time of exposing the original to light while scanning and the time of opening and closing an original cover. In addition, it has the disadvantage in that the transparent platen is cracked by the vibration of the transparent platen itself.
On the other hand, when the above described automatic original feeder is mounted on an image forming apparatus of a type of manually disposing an original on a transparent platen, a supporting member for rotatably supporting the above described frame is attached to a hole for attaching a conventional original cover on the upper surface of the main body thereof, thereby to mount the automatic original feeder to the main body of the image forming apparatus.
The position of the above mentioned hole for attaching an original cove differs by the types of image forming apparatuses. Thus, an automatic original feeder of plural specification having different arrangement of a supporting member of a frame is necessary according to the position of a hole for attaching an original cover of each type, which brings the disadvantage of cost increase.